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/*
 * =============================================================================
 * 
 *   Copyright (c) 2011-2014, The THYMELEAF team (http://www.thymeleaf.org)
 * 
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 * 
 *       http://www.apache.org/licenses/LICENSE-2.0
 * 
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 * 
 * =============================================================================
 */
package org.thymeleaf.spring4.resourceresolver;

import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.core.io.Resource;
import org.thymeleaf.IEngineConfiguration;
import org.thymeleaf.TemplateEngine;
import org.thymeleaf.context.IContext;
import org.thymeleaf.exceptions.TemplateInputException;
import org.thymeleaf.resource.IResource;
import org.thymeleaf.resource.ReaderResource;
import org.thymeleaf.resourceresolver.IResourceResolver;
import org.thymeleaf.util.StringUtils;
import org.thymeleaf.util.Validate;

/**
 * 
 *   Implementation of {@link org.thymeleaf.resourceresolver.IResourceResolver} that resolves
 *   resources by delegating on Spring's resource resolution mechanism, implemented by the
 *   {@link org.springframework.core.io.ResourceLoader} interface.
 * 
 * 
 *   This resource resolver accesses the Spring resource resolution mechanism by means of
 *   calls to {@link ApplicationContext#getResource(String)}.
 * 
 *
 * @author Daniel Fernández
 *
 * @since 2.1.0 (reimplemented in 3.0.0)
 *
 */
public final class SpringResourceResourceResolver
        implements IResourceResolver, ApplicationContextAware {

    private static final Logger logger = LoggerFactory.getLogger(SpringResourceResourceResolver.class);

    public static final String NAME = "SPRING-RESOURCE";

    private ApplicationContext applicationContext = null;



    public SpringResourceResourceResolver() {
        super();
    }


    public String getName() {
        return NAME;
    }

    public void setApplicationContext(final ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }



    public IResource resolveResource(
            final IEngineConfiguration configuration, final IContext context,
            final String resource, final String characterEncoding) {

        Validate.notNull(resource, "Resource name cannot be null");
        Validate.notNull(this.applicationContext,
                "ApplicationContext has not been initialized in resource resolver. TemplateResolver or " +
                        "ResourceResolver might not have been correctly configured by the Spring Application Context.");

        try {

            final Resource resourceObject = this.applicationContext.getResource(resource);
            if (resourceObject == null) {
                return null;
            }

            final InputStream inputStream = resourceObject.getInputStream();
            if (inputStream == null) {
                return null;
            }

            final InputStreamReader reader;
            if (!StringUtils.isEmptyOrWhitespace(characterEncoding)) {
                reader = new InputStreamReader(inputStream, characterEncoding);
            } else {
                reader = new InputStreamReader(inputStream);
            }

            return new ReaderResource(resource, reader);

        } catch (final UnsupportedEncodingException e) {
            throw new TemplateInputException("Exception reading resource: " + resource, e);
        } catch (final Throwable t) {
            showException(resource, t);
            return null;
        }

    }



    private static void showException(final String resourceName, final Throwable t) {
        if (logger.isDebugEnabled()) {
            if (logger.isTraceEnabled()) {
                logger.trace(
                        String.format(
                                "[THYMELEAF][%s] Resource \"%s\" could not be resolved. This can be normal as " +
                                        "maybe this resource is not intended to be resolved by this resolver. " +
                                        "Exception is provided for tracing purposes: ",
                                TemplateEngine.threadIndex(), resourceName),
                        t);
            } else {
                logger.debug(
                        String.format(
                                "[THYMELEAF][%s] Resource \"%s\" could not be resolved. This can be normal as " +
                                        "maybe this resource is not intended to be resolved by this resolver. " +
                                        "Exception message is provided (set the log to TRACE for the entire trace): " +
                                        "%s: %s",
                                TemplateEngine.threadIndex(), resourceName,
                                t.getClass().getName(), t.getMessage()));
            }
        }
    }


}